Syringe and catheter apparatus

ABSTRACT

To inflate the balloon element on the distal end of a pulmonary artery catheter an improved gas syringe is provided which is both volume and pressure-limited so that the syringe is capable of discharging into the catheter no more than the maximum design gas inlet volume thereof while at the same reducing the maximum attainable pressure within the catheter to a predeterminable level substantially below that reached when a conventional volume-limited syring of the same gas discharge capacity is used. The syringe volume delivery limitation is achieved by forming rearwardly disposed plunger stop members, or a suitable vent opening, in a sidewall portion of the syringe body. The pressure limitation is obtained by forming a pressure absorption zone which defines a substantially inextensible enlargement of the gas-receiving interior of the catheter. In one embodiment of the invention the pressure absorption zone is created in a forward end portion of the syringe body by a hollow stop member positioned therein, or inwardly projecting stop portions formed thereon, which engage and stop the syringe plunger rearwardly of the forward endwall of the syringe body. In an alternate embodiment, the forward plunger stop portion is deleted and the pressure absorption zone is formed externally to the syringe body by a length of tubing interconnected between the syringe outlet and the gas-receiving inlet of the catheter.

BACKGROUND OF THE INVENTION

The present invention relates generally to medical devices, and moreparticularly provides an improved syringe and inflatable catheterapparatus which incorporates a uniquely configured volume andpressure-limited gas syringe used to internally pressurize the catheterportion of the apparatus.

Potential over-pressurization of inflatable catheter elements used tointernally block various body passages, such as the pulmonary artery, isa well known and long-standing problem in the practice of medicine.Pulmonary artery catheters are typically provided at their distal endwith a small balloon which is selectively inflatable by a gas syringeconnected to the catheter's gas-receiving inlet. To utilize thecatheter, a sheath element is inserted into a suitable vein, such as thejugular vein, and the distal end of the catheter is fed through thesheath into the vein. When the distal end of the catheter exits theinner end of the sheath, the balloon is inflated. The inflated balloonacts as a "float" to assist in further insertion of the catheter bydrawing its distal end through the vein (by virtue of the blood flowtherethrough) and ultimately into a position in which the inflatedballoon becomes "wedged" in a branch of the pulmonary artery. Lodged ina pulmonary artery branch in this manner the distal end of the cathetermay be utilized in a conventional manner to monitor the pulmonary artery"wedge" pressure via the resulting pressure trace pattern on anoscilloscope operatively connected to the catheter.

After this initial wedge pressure reading is taken the balloon isdeflated, but the catheter is normally left in place so that the balloonmay be re-inflated to take subsequent wedge pressure readings. Theover-pressurization problem previously mentioned typically arises when,between these intermittent balloon inflations, the distal catheter end"migrates" into a smaller portion or branch of the pulmonary artery.Subsequent balloon inflation then takes place in an unintended arterialportion which may be weaker and/or of a smaller interior cross-sectionthan anticipated. If great care is not exercised in re-inflating thecatheter balloon in these instances, the balloon can be over-pressurizedand cause the artery to burst.

Typically, the catheter has a design inlet gas volume capacitycorresponding to the gas volume required to fully inflate the balloon.In a variety of conventional manners the syringe is volume-limited toassure that no more than this designed-for gas volume can be forced intothe catheter from the syringe to thereby prevent over-inflation of theballoon.

However, even with this volume "matching" between the syringe andcatheter it is possible to cause over-pressurization of the catheterballoon during the intermittent reinflation thereof, and concomitantrupture of the artery portion into which it has migrated, if the syringeis not correctly and carefully used by its operator. Specifically,during each subsequent reinflation of the balloon the syringe plungermust be moved slowly toward the end of its stroke within the syringebody to avoid inordinately high "peak" pressures in the inflatingballoon. Even the proper slow movement of the syringe plunger can causethe balloon to rupture the smaller or weaker artery portion if theplunger is pushed too far and too hard by the syringe operator.

The operational safety of conventional pulmonary artery catheters (aswell as other types of syringe-operated inflatable catheters) is thus toa large degree dependent upon the "feel" transmitted to the syringeplunger as the catheter interior pressure is being increased, and thesyringe operator's skill in interpreting and reacting to such "feel".Even though the pressure trace on the catheter-connected oscilloscopewill normally indicate when the artery portion has been sufficientlyoccluded by the inflating balloon (by generating a recognizable "wedge"pattern), certain heart infirmities (such as an incompetent mitralvalve) can generate a potentially misleading trace pattern which, eventhough the partially inflated balloon is fully blocking the arteryportion, indicates that further balloon inflation is needed. It is thisfurther balloon inflation which, in conventional volume-limited syringeand catheter apparatus, can easily burst the artery.

Various attempts have been previously made to eliminate thisover-pressurization problem. For example, as exemplified in U.S. Pat.Nos. 3,642,005; 3,905,361 and 4,064,882 inflatable external indicatorballoons have been placed on non-inserted portions of catheters toprovide the syringe operator with an additional visual indication of thedegree of inflation reached in the internal catheter balloon. Othersupplemental visual internal catheter pressure indicia, such as simplepressure gauges have also been utilized. These and other visuallyoriented safety devices, however, must (along with the oscilloscopetrace pattern) be continually watched by the syringe operator, andproperly reacted to, to be effective. Also, particularly in the case ofpressure gauges, moving parts are involved which are always subject tomalfunction and wear.

Other mechanical devices, such as pressure relief valves, have also beenused to actually limit the pressure supplied to the catheter.Illustrative devices of this type may be found in U.S. Pat. Nos.3,871,374; 4,116,201 and 4,439,185. Other representative syringe andcatheter devices may be found in U.S. Pat. Nos. 4,335,723; 4,370,982 and4,583,974. The problem with mechanical pressure-limiting devices such asmulti-component pressure regulators or relief valves is that they aresubject, like all devices with moving parts, to malfunction or failure.

It can be seen from the foregoing that a long-standing need exists forimproved syringe and inflatable catheter apparatus having greateroperational safety from a catheter over-pressurization standpoint.Accordingly, it is an object of the present invention to provide suchapparatus.

SUMMARY OF THE INVENTION

In carrying out principles of the present invention, in accordance witha preferred embodiment thereof, improved syringe and catheter apparatusis provided which comprises a catheter having an inflatable element suchas a balloon on its distal end and an improved gas syringe which isconnectable to the catheter and operable to inflate the distal endballoon thereon. The syringe is uniquely provided with both volume andpressure limiting means which cooperatively function to permit thesyringe to force up to the maximum design volume of pressurized gas intothe catheter while automatically reducing the maximum attainable gaspressure within the catheter (and thus the balloon) to a predeterminedlevel well below that attainable when utilizing a conventional syringewith the same maximum gas volume discharge capability.

The volume limiting means in the improved syringe of the presentinvention are of generally conventional construction and may compriseeither rearwardly disposed plunger stops formed within the syringe bodyto limit the rearward travel of the syringe plunger, a rearwardlydisposed vent opening formed through a sidewall portion of the syringebody, or other suitable volume limiting means. In any event, the volumelimiting means function to assure that no more than the maximum designgas volume of the catheter can be forced thereinto from the syringe.

The pressure limiting or pressure reducing means in the improved syringefunction to create therein a pressure absorption zone which defines asubstantially inextensible enlargement of the gas-receiving interior ofthe catheter. This volume enlargement creates, in effect, a "dead space"which reduces to a predetermined level the pressure rise within thecatheter associated with its receipt of its design gas volume from thesyringe. In the preferred embodiment of the present invention thepressure limiting means comprise forward stop means, disposed within thesyringe body, for engaging and stopping the syringe plunger duringforward travel thereof at a position spaced rearwardly from the forwardendwall of the syringe body. By limiting the forward movement of thesyringe plunger in this fashion the pressure absorption zone is formedwithin a forward end portion of the improved syringe. In one version ofthis improvement the forward stop means are defined by a hollowcylindrical stop member coaxially disposed within a forward end portionof the syringe body. In another version the forward stop means areformed by diametrically opposed, radially inwardly projecting sidewallportions of the syringe body which are spaced rearwardly from theforward endwall of the body.

In an alternate embodiment of the present invention the forward stopmeans are deleted from the syringe and the unique pressure absorptionzone is formed externally to the syringe by a length of tubingoperatively interconnected between the syringe outlet and thegas-receiving inlet of the catheter and having an interior volume equalto the desired volume of the pressure absorption zone.

The present invention conveniently permits the conversion of a standardsyringe, having an internal volume greater than the design volume of aparticular catheter, to a volume and pressure-limited syringe whosemaximum dischargeable gas volume is precisely matched to the maximumdesign inlet volume of the catheter while at the same time reducing to amuch safer, and predeterminable, level the maximum pressure attainablewithin the catheter. This conversion is easily and inexpensivelyachieved by simply forming the previously described volume limitingmeans on the syringe body and appropriately creating the pressureabsorption zone either within the syringe body via the forward stopmeans, or externally to the body by using an appropriately sized lengthof interconnecting tubing.

Importantly, the unique operational safety improvement provided by thepresent invention is achieved without the addition of any complex,moving or wear-prone mechanical parts to the syringe and catheterapparatus such as mechanical pressure regulators, pressure reliefvalves, pressure gauges or external balloon inflation indicators.Moreover, other than the usual catheter-connected oscilloscope, there isno need for supplementary visual pressure-monitoring apparatus (such aspressure gauges or external balloon elements) which must be carefullyand continuously watched by the syringe operator. All of thesepreviously utilized mechanical pressure-monitoring devices are uniquelyeliminated in the present invention due to its provision of thecooperating volume limiting means and the pressure absorption zone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectioned and exploded fragmentary sideelevational view of an improved syringe and catheter apparatus whichembodies principles of the present invention;

FIG. 1A is a partially sectioned side elevational view of a rear endsection of an alternate embodiment of the syringe portion of theapparatus;

FIG. 2 is a perspective view of a hollow cylindrical pressure-limitingmember disposed within the syringe of FIG. 1;

FIG. 2A is a perspective view of an alternate embodiment of thepressure-limiting member;

FIG. 3 is an enlarged scale cross-sectional view through the syringe,taken along line 3--3 of FIG. 1, and illustrates the pressure-limitingmember of FIG. 2 disposed therein;

FIG. 3A is an enlarged scale cross-sectional view similar to that ofFIG. 3, but with the pressure-limiting member of FIG. 2A disposed in thesyringe;

FIG. 4 is an enlarged scale cross-sectional view through the syringetaken along line 4--4 of FIG. 1;

FIG. 5 is a partially sectioned side elevational view of a forward endportion of a further alternate embodiment of the syringe; and

FIG. 6 is a partially sectioned and exploded fragmentary sideelevational view of an alternate embodiment of the syringe and catheterapparatus.

DETAILED DESCRIPTION

Depicted in FIG. 1 is an improved syringe and catheter apparatus 10which embodies principles of the present invention and comprises apulmonary artery catheter 12, of conventional construction, and auniquely configured syringe 14 which is utilized in a mannersubsequently described to force air (or another, more readily solublegas such as carbon dioxide) into the catheter 12. The representativecatheter 12 illustrated in FIG. 1 is of the "quadruple lumen" typehaving, at its proximal or inlet end, four tubes or "lumens" 16, 18, 20,and 22 which are operatively interconnected to a single insertion tube24 by means of a suitable connector fitting 26. Secured to the insertiontube 24, adjacent its distal end 28, is a small latex balloon member 30which is inflatable to the dashed line configuration 30_(a) in responseto the receipt of pressurized gas within the lumen 16 from the syringe14. Pressurized syringe gas received within the lumen 16 is flowed intothe balloon 30 via an internal passage (not illustrated) within theinsertion tube 24 and a small slit 32 formed in the tube 24 andenveloped by the balloon.

At its outer end, the gas inlet or balloon inflation lumen 16 isprovided with an inlet fitting 34 having a gas inlet passage 36 flankedby a pair of small connecting tabs 38, and a gas shutoff valve member 40which is slidable relative to the balance of the inlet fitting 34, asindicated by the double-ended arrow 42, to selectively open and closethe gas inlet passage 36. The other three lumens 18, 20 and 22, whichplay no direct role in the present invention, respectively comprise aproximal injection lumen, a distal lumen, and a thermistor lumen. Thesethree lumens are utilized in a conventional manner to monitor variouscharacteristics within the pulmonary artery and right heart into whichthe inflatable portion 24 of the catheter 10 is inserted as subsequentlydescribed.

Syringe 14 has a hollow, transparent plastic body 42 of an elongatedcylindrical configuration. Body 42 has a forwardly disposed, conicalinner or outlet endwall 44, and an open rear or outer end 46 havingoutwardly projecting finger support tabs 48 formed thereon. Extendingaxially outwardly from the forward endwall 44, and communicating withthe interior of the syringe body 42, is a reduced diameter, hollowcylindrical outlet tube 50. Coaxially circumscribing the outlet tube 50is a larger diameter hollow cylindrical connection collar 52 whichprojects outwardly from the endwall 44. The collar 52 is somewhatshorter than the outlet tube 50 and is internally threaded as at 54.

The catheter 12 is connectable to the syringe 14 by inserting the outlettube 50 into the gas inlet passage 36 of the catheter inlet fitting 34so that the connecting tabs 38 enter the syringe connecting collar 52.The syringe body 42 and the catheter inlet fitting 34 are thenrelatively rotated so that the connecting tabs 38 engage the internalthreads 34 to thereby releasably lock the inlet fitting 34 to theconnecting collar 52.

To pressurize gas within the syringe body 42 and force the gas into theballoon inflation lumen 16, the syringe 14 is provided with a plunger 56which is coaxially received within the syringe body 42 for movementtoward and away from the syringe body endwall 44 (as may be seen bycomparing the solid line position of the plunger to its dotted lineposition 56_(a)) to respectively force gas from and draw gas into thesyringe body. Plunger 56 has an elongated plastic body portion 58defined in cross-section by four longitudinally extending transverseribs 60 (see also FIG. 4). At its outer end the plunger body 58 isprovided with a circular thumb flange 62, while at the inner end of theplunger body is a smaller diameter circular flange 64. Secured to theinner end of the plunger body 58, and abutting its inner end flange 64,is a rubber seal element 66 which slidably and sealingly engages theinterior surface of the syringe body 42 and has a generally conicallyshaped inner end portion 68 that is complementarily configured relativeto the endwall 44.

To utilize the syringe and catheter apparatus 10, the tube portion 24thereof is inserted into and through a suitable vein, such as thejugular vein, until the distal end 28 of the insertion tube 24 isproperly positioned within the superior vena cava. The syringe plunger56 is then manually pushed toward the syringe body endwall 44 to inflatethe balloon 30. Balloon 30 is then "floated" through the heart and intothe pulmonary artery until a branch thereof is occluded by the inflatedballoon. With a pulmonary artery branch blocked in this manner, avariety of conditions therein, such as the "wedge" pressure downstreamfrom the distal tube end 28 may be measured and monitored. This initialmeasurement and monitoring (as well as subsequent measurement andmonitoring) is effected by an oscilloscope which is operativelyassociated with the catheter and generates a trace pattern indicative ofthe arterial wedge pressure downstream from the inflated balloon.

After this initial wedge pressure reading has been taken, the balloon isdeflated. However, the catheter is then normally left in its insertedposition so that the balloon can be selectively reinflated to takesubsequent wedge pressure and/or other readings. It is primarily inconjunction with these subsequent balloon inflations that the well-knownproblem of balloon over-pressurization, and concomitant bursting of apulmonary artery branch can occur.

This problem can arise if, after the initial deflation of the balloon,the distal catheter end "migrates" into an arterial branch which issubstantially smaller and/or weaker than the one the inflated ballooninitially became wedged in and occluded. Subsequent inflation of theballoon in this smaller and/or weaker arterial branch, if not done withextreme care, can easily cause the arterial branch to rupture and causevery rapid death of the patient.

Arterial catheters, such as the representative catheter 12 depicted inFIG. 1, are typically designed (and so labeled) to receive up to apredetermined maximum volume of pressurized air (or other gas) from itsassociated syringe-such volume of gas being that which will fullyinflate the balloon 30 or other inflatable element associated with theinsertion tube 24. Subject to the expected variations in interior sizesof pulmonary arteries, and the strengths thereof, this overall volumedesign limitation is intended to safely limit the maximum balloonpressure.

As an example, the illustrated catheter 12 has a 1.5 cc volume designlimitation. Typically, conventional syringes used in conjunction withcatheters of this type have an internal body volume greater than thedesign volume of the catheter. This is due to the fact that it isconvenient, and less expensive, for the apparatus manufacturer toutilize a single, standard-sized syringe body with a variety ofcatheters having varying volume design capacities. As an example, thesyringe 14 depicted in FIG. 1 in conjunction with the 1.5 cc catheter 12has a nominal gas discharge capacity of 5 cc-i.e., a gas dischargecapacity substantially larger than the design limit of catheter 12.

In an attempt to safely "match" the over-sized syringe to the catheter,it has been conventional practice to provide the syringe withvolume-limiting means which function to limit the maximum gas volumedischargeable therefrom to the nominal volume inlet capacity of thecatheter. In conventional over-sized catheter syringes, suchvolume-limiting means are provided by forming in the side wall portionof the syringe body laterally inwardly directed, diametrically opposedprojections 70 which are positioned forwardly of the open body end 46and rearwardly of the plunger body flange 64. The projections 70 arenormally formed by pressing heated cylindrical forming members againstdiametrically opposite sidewall portions of the syringe body toplastically deform such sidewall portions into the syringe body so thatthey project inwardly of the periphery 72 (FIG. 4) of the plunger bodyflange 64. Positioned in this manner, the inward projections 70 functionas stop members which limit the rearward travel of the plunger withinthe syringe body.

In a conventionally constructed catheter syringe of this type, theseprojections are axially positioned on the syringe body so that the gasvolume within the syringe body between the plunger seal element and theoutlet endwall of the body is equal to the nominal volume capacity ofthe catheter. Thus, the dischargeable gas quantity of the syringe isprecisely matched to the design volume capacity of the catheter. Asillustrated in FIG. 1, this volume-limiting technique, via thepreviously described stop members 70, is incorporated into the improvedsyringe 14 of the present invention. However, for reasons subsequentlydescribed, the distance between the illustrated stop members 70 and theendwall 44 is greater than such distance in catheter syringes ofconventional construction.

A modified conventional volume-limiting technique is also incorporatedin the alternate embodiment 14_(a) of the syringe 14 depicted in FIG.1A, the syringe 14_(a) being in all other regards identical to thesyringe 14. In the syringe 14_(a), the rearwardly disposed plunger stopmembers 70 are eliminated, and are replaced by a small vent opening 74formed through the sidewall of the syringe body forwardly of the openrear end 46 thereof. It can be seen in FIG. 1A that with the plungerseal element 66 disposed rearwardly (i.e., leftwardly) of the opening74, forward motion of the plunger 56 toward the opening 74 will notforce pressurized gas from within the syringe body into the catheterlumen 16. Instead, such forward plunger motion will simply force gasfrom within the syringe body outwardly through the vent opening 74.

It is only when the forwardmost annular sealing surface 76 of the sealelement 66 forwardly crosses the opening 74 that the plunger can forcepressurized gas outwardly through the outlet end of the syringe and intothe lumen 16. Accordingly, in conventional catheter syringes, the ventopening 74 is axially positioned along the length of the syringe bodysuch that the volume between the opening and the outlet endwall of thesyringe body is equal to the design volume capacity of the catheter.However, as in the case of the rear stop members 70 in syringe 14, theopening 74 in syringe 14_(a) is spaced a greater distance rearwardlyfrom the endwall 44 than it would be in a conventional syringe havingthe same gas discharge capacity.

In and of itself, however, neither of these conventional volume-limitingmeans (or other similar volume-limiting means) completely eliminates thepotential problem of over pressurizing the balloon 30 when it isdisposed within an artery having a lesser strength or internal dimensionthan anticipated when, for example, the uninflated catheter has distallymigrated. In these instances, even though no more than the catheterdesign gas volume can be forced thereinto from the syringe,overpressurization of the catheter balloon, and arterial rupture, canoccur.

Typically, upon each re-inflation of the catheter balloon the syringeoperator must carefully and slowly depress the syringe plunger until theoscilloscope trace pattern indicates a "wedge" condition has beenachieved--i.e., the inflating balloon has occluded the arterial branchin which it is lodged. At this point (which normally occurs with theballoon in a partially inflated condition) the syringe operator mustdesist from further inflating the balloon.

However, as is well known, the configurations of both "normal" and"wedge" trace patterns on the monitoring oscilloscope vary widely frompatient to patient and can occasionally mislead even experienced syringeoperators as to the existence of balloon occlusion in the artery branchin which the balloon is disposed. More specifically, the trace patternmay closely resemble one which is normally indicative of a nonoccludedartery when, in fact, full occlusion exists and further ballooninflation could rupture the artery. As but one example, an incompetentmitral valve can generate back pressure pulses which can misleadinglyindicate that the distal catheter end is still "free" within the arteryeven though it is fully blocking the artery.

It is in these instances when great care must be exercised in inflatingthe catheter balloon. The syringe operator must be acutely aware of theresistance of the syringe plunger to further forward travel and stop itsfurther travel if too great a resistance is encountered. In other words,the operator must rely on the "feel" of the syringe plunger to safeguardagainst arterial rupture because even in volume-limited syringes ofconventional construction excessive pressures can easily be generatedwithin the occluding balloon.

In a preferred embodiment thereof the present invention uniquely andsubstantially reduces these potential balloon overpressurizationproblems by providing within the body 42 of syringe 14 (or syringe14_(a) as the case may be) a stop member 80 which, in conjunction withthe volume-limiting means 70 (or 76) affords the syringe theadvantageous capability of being able to force into the catheter 12 upto its designed-for maximum volume of pressurized gas (to thereby fullyinflate the balloon 30 during its blood-drawn initial "float" throughthe heart) while at the same time automatically reducing to apredetermined magnitude the pressure within the balloon 30 when itreceives this maximum volume of gas from the syringe.

Referring to FIGS. 1-3, the stop member 80 has a hollow cylindrical body82 whose external diameter is somewhat smaller than the internaldiameter of the syringe body 42. At one end thereof the body 82 iscircumferentially enlarged to define an annular end flange 84. The stopmember 80 is coaxially disposed within a forward end portion of thesyringe body so that the flange 84 abuts a radially outer portion of theconical endwall 44 and the opposite annular end surface 86 of the stopmember faces the plunger seal element 66.

Interposed in this manner between the seal element 66 and the syringeoutlet tube 50, the stop member 80 creates within the syringe body 42 apressure absorption zone which defines an essentially inextensibleenlargement of the gas-receiving interior of the catheter 12. Suchpressure absorption zone comprises the annulus 88 circumscribing thestop member body 82, the interior 90 of the body 82, and the generallyconical space 92 disposed between the flange 84 and the syringe bodyendwall 44. The end surface 86 of the stop member 80 engages and stopsthe plunger seal element 66 during forward movement thereof in aposition (indicated at 66_(a) in FIG. 1) spaced rearwardly from thesyringe body endwall 44.

This end surface 86 is suitably spaced from the stop members 70 so thatwhen the plunger seal element 66 moves from its solid line position toits dotted line position 66_(a) a maximum of 1.5 cc of pressurized gas(i.e., the maximum design volume of the catheter 12) is forced throughthe stop member interior 90 and the outlet tube 50 into the lumen 16 andthe insertion tube 24 to thereby fully inflate the balloon 30.

However, since the total effective volume of the gasreceiving interiorof the catheter 12 is increased by the pressure absorption zone volumecreated by the stop member 80, the resulting internal pressure withinthe balloon 30 is reduced by a preselected magnitude determined by thesize of the stop member 80. By properly selecting the maximum attainablepressure within the balloon 30, the risk of rupturing an artery which issmaller or weaker than anticipated is substantially reduced.Importantly, such risk is effectively reduced without regard to how theplunger 56 is pushed or who is pushing it.

The syringe 14_(a) of FIG. 1A is functionally identical to the syringe14, in that it is both volume and pressure-limited, except that thevolume-limiting wall opening 74 does not form a rearward mechanical stopfor the plunger 56. Instead, as previously described, it functions(together with the forward stop member 80) to limit the "effective"stroke of the plunger since internal pressurization of the syringe bodydoes not begin until the sealing surface 76 of the seal elementforwardly traverses the wall opening 74.

It should be noted that the actual maximum stroke of the plunger 56 insyringe 14 (or the maximum "effective" plunger stroke in syringe 14_(a))necessary to discharge the maximum design gas volume into the catheter12 is at least somewhat longer than would otherwise be necessary in theabsence of the stop member 80. This is due to the fact that thegas-receiving interior of the catheter 12 has been effectively increasedby the volume of the pressure absorption zone defined by the stop member80. Accordingly, more gas must be displaced within the syringe body bythe plunger seal element 66 to flow the design volume of gas into thecatheter, and the distance between the stop members 70 (or the opening74) and the endwall 44 is concomitantly increased. It will beappreciated that the necessary spacing between the stop member endsurface 86 and the rear stop members 70, or the side-wall opening 74, isdetermined by the total volume of the pressure absorption zone createdby the stop member 80.

It will be readily appreciated that the stop member 80 may be given avariety of alternate configurations other than that depicted in FIG. 2.As but one example of such alternate configuration, an alternate forwardstop member 80_(a) (FIGS. 2A and 3A) may be provided which has a hollowcylindrical configuration of an external diameter just slightly smallerthan the internal diameter of the syringe body 42 so that the stopmember 80_(a) is closely received in the syringe body adjacent itsendwall 44 as cross-sectionally depicted in FIG. 3A. It can be seen thatthis embodiment of the forward stop member, when positioned within thesyringe body, defines a radially inward enlargement of a forward axialportion thereof. Accordingly, instead of inserting the stop member80_(a) into the syringe body, a forward longitudinal portion of the bodycould simply be enlarged during its manufacture.

Alternatively, in conjunction with the modified syringe embodiment14_(b) illustrated in FIG. 5, inserts such as stop members 80 and 80_(a)could be replaced by diametrically opposed, inwardly projecting forwardstop portions 94 formed in the sidewall of the syringe body 42, in amanner similar to that used to form the stop portions 70 in FIG. 1, andpostioned rearwardly of the syringe body endwall 44 and forwardly of theplunger seal element 66. In this instance, the pressure absorption zonewould be defined by the interior syringe body volume 96 positionedbetween the outlet tube 50 and the forward conical face 68 of theplunger seal element 66 when it sealingly engages the forward stopmembers 94 as depicted in FIG. 5.

In the previously described embodiments of the improved syringe of thepresent invention, the unique pressure absorption zone was createdwithin the syringe body by forward stop means therein such as theelements 80, 80_(a) or 94. However, if desired, such pressure absorptionzone may be formed externally to the syringe body. Referring now to FIG.6, an alternate embodiment 10_(a) of the syringe and catheter apparatus10 is illustrated in which a modified syringe 14_(c) is provided that issimilar in construction to the previously, described syringes, and hasvolume-limiting means such as stops 70 or wall opening 74, but hasremoved therefrom the forward stop means. Accordingly, the conical endsurface 68 of the plunger seal element 66 may be forced into engagementwith the complementarily configured interior surface 44_(a) of theoutlet endwall 44.

The external pressure absorption zone is defined by a length of plastictubing 96 which has an internal volume equal to the desired volume ofthe pressure absorption zone and is interconnectable between the syringeoutlet tube 50 and the catheter inlet fitting 34. Specifically, thetubing 96 has a female inlet fitting 98 adapted to receive the outlettube 50, and a male discharge fitting 100 adapted for insertion into thegas inlet passage 36 of the catheter inlet fitting 34. While the plastictubing 96 is flexible, when it is operatively interconnected between thesyringe and the catheter as previously described it defines anessentially inextensible enlargement of the gas-receiving interior ofthe catheter. In this manner, when the end face 68 of the plunger sealelement 66 engages the interior surface 44_(a) of the endwall 44 the 1.5cc design gas volume will have been forced into the catheter, but theresulting balloon pressure will be lessened to a predetermined degree bythe pressure absorption zone defined within the interconnecting tube 96.The syringe 14c, like the previously described syringes 14, 14_(a) and14_(b), is thus both volume and pressure-limited.

As previously mentioned, the present invention may be convenientlyutilized in conjunction with a gas syringe having a "standard" body sizewith a total internal volume in excess of that needed to provide thecatheter with its maximum design volume of gas to fully inflate itsballoon element. By providing the standard syringe body with appropriatevolume-limiting means (such as stops 70 or wall opening 74) togetherwith the unique pressure reducing means of the present invention (suchas the elements 80, 80_(a), 94 or 96) it may be inexpensively convertedto a volume and pressure-limited syringe such as the syringes 14,14_(a), 14_(b) and 14_(c). By appropriate correlation between the volumeof the pressure absorption zone, the desired reduction in final balloonpressure and the rearward spacing of the volume-limiting means, astandard size syringe body may be conveniently converted for use withcatheters having a variety of maximum gas volume requirements.

However, if desired, the syringe body may be custom size for eachcatheter application so that the necessity for the previously describedvolume limiting means is eliminated. This could be achieved for example,by simply shortening the syringe body length so that (with the pressurereducing means in place) the resulting maximum effective availableplunger stroke could discharge from the syringe only the design gasvolume of the catheter.

It can be seen that the present invention provides an improved syringeand catheter apparatus having significantly enhanced operational safetycharacteristics. The maximum balloon pressure achievable with the volumeand pressure-limited syringe may be reduced to a predetermined, saferlevel without the previous necessity of utilizing pressure reliefvalves, external inflatable elements or other conventional pressurelimiting devices which are subject to wear and/or failure during use.Additionally, other than the normal necessity of monitoring theoscilloscope for the "wedge" trace pattern during reinflation of thecatheter balloon, there is no need to otherwise monitor the pressureincrease within the catheter, as with a mechanical pressure gauge, sincethe maximum pressure attainable therein is preset, and nonvariable, byvirtue of the unique pressure absorption zone within the apparatus.

While the principles of the present invention are particularly welladapted for use in conjunction with the illustrated pulmonary arterycatheter, it will be appreciated that such principles may also beutilized in other gas-operated catheter apparatus such as, for example,endotracheal catheters which are provided at their distal ends withinflatable cuff members.

The foregoing detailed description is to be clearly understood as beinggiven by way of illustration and example only, the spirit and scope ofthe present invention being limited solely by the appended claims.

What is claimed is:
 1. Improved syringe and catheter apparatuscomprising:catheter means for internally blocking a body passage, saidcatheter means being adapted to internally receive a predeterminedmaximum volume of pressurized gas from a source thereof and having aninflatable portion insertable into the body passage for inflationtherein by the pressurized gas received within said catheter means;syringe means operable to discharge up to said predetermined maximumvolume of pressurized gas into the interior of said catheter means; andpressure reducing means positioned within said syringe means fordefining an essentially inextensible enlargement of the gas-receivinginterior of said catheter means, said enlargement functioning as apressure absorption zone which reduces to a predetermined magnitude themaximum internal pressure within the gas receiving interior of saidcatheter means caused by receipt therein of said predetermined maximumvolume of pressurized gas from said syringe means so that saidpredetermined maximum volume of pressurized gas may be forced into andretained within the gas-receiving interior of said catheter meanswithout creating therein a pressure exceeding said predeterminedmagnitude thereof, said syringe means including a hollow syringe bodyand said pressure absorption zone being disposed within said body andbounded by an interior surface portion thereof, said syringe meansfurther including a plunger disposed in said hollow syringe body andoperative to force gas therein outwardly through an outlet thereof, saidpressure reducing means including stop means, positioned within saidhollow syringe body between said plunger and said outlet, for engagingand stopping said plunger in a spaced relationship with said outletduring movement of said plunger toward said outlet, said stop meansdefining an internal enlargement of said hollow syringe body.
 2. Theapparatus of claim 1 wherein:said internal enlargement is positionedadjacent said outlet.
 3. The apparatus of claim 1 wherein:said internalenlargement is spaced apart from said outlet.
 4. Improved syringe andcatheter apparatus comprising:catheter means for internally blocking abody passage, said catheter means being adapted to internally receive apredetermined maximum volume of pressurized gas from a source thereofand having an inflatable portion insertable into the body passage forinflation therein by the pressurized gas received within said cathetermeans; syringe means operable to discharge up to said predeterminedmaximum volume of pressurized gas into the interior of said cathetermeans; and pressure reducing means positioned within said syringe meansfor defining an essentially inextensible enlargement of thegas-receiving interior of said catheter means, said enlargementfunctioning as a pressure absorption zone which reduces to apredetermined magnitude the maximum internal pressure within the gasreceiving interior of said catheter means caused by receipt therein ofsaid predetermined maximum volume of pressurized gas from said syringemeans so that said predetermined maximum volume of pressurized gas maybe forced into and retained within the gas-receiving interior of saidcatheter means without creating therein a pressure exceeding saidpredetermined magnitude thereof,said syringe means including a hollowsyringe body and said pressure absorption zone being disposed withinsaid body and bounded by an interior surface portion thereof, saidsyringe means further including a plunger disposed in said hollowsyringe body and operative to force gas therein outwardly through anoutlet thereof, said pressure reducing means including stop means,positioned within said hollow syringe body between said plunger and saidoutlet, for engaging and stopping said plunger in a spaced relationshipwith said outlet during movement of said plunger toward said outlet,said stop means comprising a hollow stop member disposed within saidhollow syringe body.
 5. Improved syringe and catheter apparatuscomprising:catheter means for internally blocking a body passage, saidcatheter means being adapted to internally receive a predeterminedmaximum volume of pressurized gas from a source thereof and having aninflatable portion insertable into the body passage for inflationtherein by the pressurized gas received within said catheter means;syringe means operable to discharge up to said predetermined maximumvolume of pressurized gas into the interior of said catheter means; andpressure reducing means positioned within said syringe means fordefining an essentially inextensible enlargement of the gas-receivinginterior of said catheter means, said enlargement functioning as apressure absorption zone which reduces to a predetermined magnitude themaximum internal pressure within the gas receiving interior of saidcatheter means caused by receipt therein of said predetermined maximumvolume of pressurized gas from said syringe means so that saidpredetermined maximum volume of pressurized gas may be forced into andretained within the gas-receiving interior of said catheter meanswithout creating therein a pressure exceeding said predeterminedmagnitude thereof,said syringe means including a hollow syringe bodyhaving an internal volume greater than said predetermined maximum volumeof pressurized gas, a gas outlet formed in said hollow syringe body, anda plunger received in said hollow syringe body and operative to forcegas therein outwardly through said gas outlet, said apparatus furthercomprising volume limiting means carried by said syringe body forlimiting the volume of gas dischargeable by said plunger through saidgas outlet to said predetermined maximum volume of pressurized gas, saidhollow syringe body having a sidewall portion, and said volume limitingmeans comprising an opening formed through said sidewall portion andspaced apart from said gas outlet.
 6. A syringe for use in internallypressurizing a catheter, comprising:a hollow body adapted to receive aquantity of gas and having an outlet end operatively connectable to thecatheter for discharging gas thereinto from within said body; a plungerreceived in said body for movement toward and away from said outlet endthereof to respectively discharge gas through said outlet end and drawgas into said body; and pressure reducing means for limiting thepressure increase within the catheter to a predetermined magnitude whena predetermined maximum volume of gas is forced into the catheter fromsaid syringe, said pressure reducing means including stop means,interposed between said plunger and said outlet end of said body, forengaging and stopping said plunger in a spaced relationship with saidoutlet end during movement of said plunger toward said outlet end,saidstop means comprising a hollow stop member disposed within said body ofsaid syringe.
 7. The syringe of claim 6 wherein:said stop member isadjacent said outlet end of said body of said syringe.
 8. The syringe ofclaim 6 wherein:said stop member has a generally cylindricalconfiguration and is coaxially disposed within said body of saidsyringe.
 9. The syringe of claim 8 wherein:said stop member iscross-sectionally smaller than the interior of said body and has alaterally projecting portion formed thereon.
 10. The syringe of claim 9wherein:said laterally projecting portion is an annular flange.
 11. Thesyringe of claim 10 wherein:said annular flange is an end flange and ispositioned adjacent said outlet end of said body of said syringe.
 12. Asyringe for use in internally pressurizing a catheter, comprising:ahollow body adapted to receive a quantity of gas and having an outletend operatively connectable to the catheter for discharging gasthereinto from within said body; a plunger received in said body formovement toward and away from said outlet end thereof to respectivelydischarge gas through said outlet end and draw gas into said body; andpressure reducing means for limiting the pressure increase within thecatheter to a predetermined magnitude when a predetermined maximumvolume of gas is forced into the catheter from said syringe, saidpressure reducing means including stop means, interposed between saidplunger and said outlet end of said body, for engaging and stopping saidplunger in a spaced relationship with said outlet end during movement ofsaid plunger toward said outlet end, said stop means defining aninternal enlargement of said body of said syringe.
 13. The syringe ofclaim 12 wherein:said internal enlargement is positioned adjacent saidoutlet end of said body of said syringe.
 14. The syringe of claim 12wherein:said internal enlargement is spaced apart from said outlet endof said body of said syringe.
 15. A syringe for use in internallypressurizing a catheter, comprising:a hollow body adapted to receive aquantity of gas and having an outlet end operatively connectable to thecatheter for discharging gas thereinto from within said body; a plungerreceived in said body for movement toward and away from said outlet endthereof to respectively discharge gas through said outlet end and drawgas into said body; and pressure reducing means for limiting thepressure increase within the catheter to a predetermined magnitude whena predetermined maximum volume of gas is forced into the catheter fromsaid syringe, said pressure reducing means including stop means,interposed between said plunger and said outlet end of said body, forengaging and stopping said plunger in a spaced relationship with saidoutlet end during movement of said plunger toward said outlet end,saidstop means defining an internal enlargement of said body of saidsyringe, said internal enlargement being spaced apart from said outletend of said body of said syringe, said internal enlargement comprising agenerally facing duality of inwardly projecting wall portions of saidbody of said syringe.
 16. A syringe for use in internally pressurizing acatheter, comprising:a hollow body adapted to receive a quantity of gasand having an outlet end operatively connectable to the catheter fordischarging gas thereinto from within said body; a plunger received insaid body for movement toward and away from said outlet end thereof torespectively discharge gas through said outlet end and draw gas intosaid body; and pressure reducing means for limiting the pressureincrease within the catheter to a predetermined magnitude when apredetermined maximum volume of gas is forced into the catheter fromsaid syringe, said pressure reducing means including stop means,interposed between said plunger and said outlet end of said body, forengaging and stopping said plunger in a spaced relationship with saidoutlet end during movement of said plunger toward said outlet end, theinternal volume of said hollow body being greater than saidpredetermined maximum volume of gas and said syringe further comprisingvolume limiting means, carried by said body of said syringe, forcooperating with said plunger to limit the volume of gas dischargeablethrough said outlet end of said body of said syringe to saidpredetermined maximum volume of gas, said volume limiting meansincluding an opening extending laterally through a wall portion of saidbody spaced apart from said outlet end thereof.
 17. A syringe for use ininternally pressurizing a catheter, comprising:a hollow body adapted toreceive a quantity of gas and having an outlet end operativelyconnectable to the catheter for discharging gas thereinto from withinsaid body; a plunger received in said body for movement toward and awayfrom said outlet end thereof to respectively discharge gas through saidoutlet end and draw gas into said body; and pressure reducing means forlimiting the pressure increase within the catheter to a predeterminedmagnitude when a predetermined maximum volume of gas is forced into thecatheter from said syringe, said pressure reducing means including stopmeans, interposed between said plunger and said outlet end of said body,for engaging and stopping said plunger in a spaced relationship withsaid outlet end during movement of said plunger toward said outletend,the internal volume of said hollow body being greater than saidpredetermined maximum volume of gas and said syringe further comprisingvolume limiting means, carried by said body of said syringe, forcooperating with said plunger to limit the volume of gas dischargeablethrough said outlet end of said body of said syringe to saidpredetermined maximum volume of gas, said volume limiting meansincluding stop means for limiting movement of said plunger away fromsaid outlet end of said body of said syringe, said stop means beingdefined by an internal enlargement of said body of said syringe.
 18. Asyringe for use in internally pressurizing a catheter, comprising:ahollow body adapted to receive a quantity of gas and having an outletend operatively connectable to the catheter for discharging gasthereinto from within said body; a plunger received in said body formovement toward and away from said outlet end thereof to respectivelydischarge gas through said outlet end and draw gas into said body; andpressure reducing means for limiting the pressure increase within thecatheter to a predetermined magnitude when a predetermined maximumvolume of gas is forced into the catheter from said syringe, saidpressure reducing means including stop means, interposed between saidplunger and said outlet end of said body, for engaging and stopping saidplunger in a spaced relationship with said outlet end during movement ofsaid plunger toward said outlet end,the internal volume of said hollowbody being greater than said predetermined maximum volume of gas andsaid syringe further comprising volume limiting means, carried by saidbody of said syringe, for cooperating with said plunger to limit thevolume of gas dischargeable through said outlet end of said body of saidsyringe to said predetermined maximum volume of gas, said volumelimiting means including stop means for limiting movement of saidplunger away from said outlet end of said body of said syringe, saidstop means being defined by an internal enlargement of said body of saidsyringe, said internal enlargement comprising a generally facing dualityof inwardly projecting wall portions of said body of said syringe.